Project RR-03Ra - Converting a TRF201 into a rally car

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This one has been brewing for a few weeks. I have a wreck of a TRF201X I bought to rob parts from for my TRF211 3GL. It just felt like a waste being relatively complete, and I have been wondering about rally cars recently. Then the 90s Touring Car thread on the main forum got me fired up as i discovered these early 90s large scale touring cars based on Kyosho Ultima chassis. Got me thinking about a rear motor RWD car. I was also inspired by the M04RR XL project from a couple of years ago that turned an M04 into a rear motor 190mm touring car. I loved that conversion. I couldn't find a large scale body to fit straight on the TRF201 though, so I thought I would see about doing the opposite of the M04RR XL: Instead of growing an M Chassis I would shrink the TRF201. I bought some of the reversible suspension arms used lots of things like the FF03R, the TT02 Type S and the TA05. I went for these instead of the more obviously 'shrunk buggy' XV01 parts because the XV01 front arms are very narrow and the TRF201 uses a pivot block between the arm ends which I needed to use. The arms arrived and with a bit of light filing they fitted the front and went on the rear no bother at all. Track width looked to be in the 185ish range so we were on.

A TRF201 narrow arm....

I have no idea if this will work and I am learning a lot as I have only briefly owned a TA01 on road car. The wheelbase is currently 270ish. I have measured up the tub, and inspired by the guys who used part two TRF201 tubs in the straight section and stick them back together to make short course trucks, I plan to go the other way. If I use a shorty battery I can take 20ish mm out of the tub and still fit everything in. First thing will be to see if I can get the suspension working and get a functional vehicle. If I can I will strip out the tub, part it and shorten using a friend's bandsaw and stick it back together with plastic cement and some carbon strips.

As for the name, it seemed appropriate. The TRF201 and FF03 share their drive train and I am now using the FF03R suspension as a basis for this. And it's a rally conversion, so RR-03Ra.

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This one has been brewing for a few weeks. I have a wreck of a TRF201X I bought to rob parts from for my TRF211 3GL. It just felt like a waste being relatively complete, and I have been wondering about rally cars recently. Then the 90s Touring Car thread on the main forum got me fired up as i discovered these early 90s large scale touring cars based on Kyosho Ultima chassis. Got me thinking about a rear motor RWD car. I was also inspired by the M04RR XL project from a couple of years ago that turned an M04 into a rear motor 190mm touring car. I loved that conversion. I couldn't find a large scale body to fit straight on the TRF201 though, so I thought I would see about doing the opposite of the M04RR XL: Instead of growing an M Chassis I would shrink the TRF201. I bought some of the reversible suspension arms used lots of things like the FF03R, the TT02 Type S and the TA05. I went for these instead of the more obviously 'shrunk buggy' XV01 parts because the XV01 front arms are very narrow and the TRF201 uses a pivot block between the arm ends which I needed to use. The arms arrived and with a bit of light filing they fitted the front and went on the rear no bother at all. Track width looked to be in the 185ish range so we were on.

A TRF201 narrow arm....

I have no idea if this will work and I am learning a lot as I have only briefly owned a TA01 on road car. The wheelbase is currently 270ish. I have measured up the tub, and inspired by the guys who used part two TRF201 tubs in the straight section and stick them back together to make short course trucks, I plan to go the other way. If I use a shorty battery I can take 20ish mm out of the tub and still fit everything in. First thing will be to see if I can get the suspension working and get a functional vehicle. If I can I will strip out the tub, part it and shorten using a friend's bandsaw and stick it back together with plastic cement and some carbon strips.

As for the name, it seemed appropriate. The TRF201 and FF03 share their drive train and I am now using the FF03R suspension as a basis for this. And it's a rally conversion, so RR-03Ra.

Before you do anything irreversible to the chassis in the name of finding a body, I bought two unpainted Parma shells off of eBay recently from circa 1990 which might fit it as is. One is a late 80s Porsche 911 and the other is a 1990 Chrysler LeBaron. The Le Baron is 22.5cm across and has a wheelbase of approx 27cm. The Porsche is 19cm across and has a wheelbase of approx 26.5cm. Wheelbases on both are rough approximations as they do not have marked cutlines there to allow fitting to cars of slightly different lengths. To be honest I bought them without really having any plan for them and it is going to take me a long time to get round to thinking something up, so if you feel they might be of use to you then you could have one or both for the amount I paid for them, which was not much.

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B parts for the 201 as I need a bumper and battery hold down. Carbon reinforced TRF416 uprights because they weren't much different to the plastic ones. M05 rear dummy axles for the front wheels. TA05 42mm driveshafts (best guess, hope they work!) Some assorted shafts and things to resurrect the ball diff in the 201 drive train. The rest of the parts I gave in my spares.

Today I had a go at the front suspension.

Front suspension block needed a little more filing than first thought and I cut the stiffening web out of the arms between the pivot bosses. They now swing freely.

I want to use the stock TRF201 pivot setup with plain 3x35 shafts retained by the bumper and screws. This meant drilling the arms to suit

I drilled the hubs for the retaining grub screws and installed everything as per the FF03R manual. I am juggling the TRF201, FF03R and TT02 Type S manuals on this one!

You might able to spot these are 4 deg caster uprights. As rally and on road cars have virtually no caster and the XV01 gets 10 from its TRF 4WD buggy uprights, the 25 deg built in to the 201 seemed potentially excessive. No idea, but that was the thinking. The uprights mounted swinging forwards give 21 deg.

Next issue! The c hub hits the arms with the arm pretty much level. Clearly they didn't consider rally in the design of the TRF416!

Having read up on rally conversions of the TT02 Type S I knew a bit of dremel action would be required on the cross member.

I took a fair amount of material out to get the c hub what looked like level with a bit of droop on the arms. This is all by eye as I don't have the wheels yet.

Next problem is that the camber link angle is so steep when using the regular inner ball position that it hardly allows any suspension movement before the rod end hits the c hub. The first idea I had was to lift the inner ball right up. I trial fitted it with a 27mm long screw from the underside of the tub end mount with a load of shock spacers and a ball nut. I then fitted the cva front shock and found I needed the longest 70mm option to reach the arms.

Still wouldn't allow full shock travel at the c hub end, plus the geometry is all wrong. By the way the turnbuckle is a 3x23 spare from a TT02B kit.

(click on the above image. It's a Flickr hosted video)

After going for a ride this afternoon another solution popped into my head. Use a 20mm long counter sunk screw and a ball nut with a spacer to replaced the ball screw in the c hub. I was too concerned about the lack of thread engagement on the ball screw to add the spacer to that.

Dropped the other side down to a 20mm screw.

(Click on the video)

I am not sure the c hub pivot will clear the wheel rim, guess we will see. Ideally would like to drop the inner ball some more but that will limit travel. I have no idea if this much travel is excessive for a rally car. We'll find out!

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Rear suspension mocking up this morning. Rear arms on the stock TRF201 pivots. 5.5mm of spacers needed to hold them in place. Purple bits are Schumacher Speed Pack 3mm spacers. Considerably better value than the equivalent Tamiya 5.5mm pack which are the same size.

Rear uprights. Reinforced TRF416. The later 418 parts only have a single hole on top so I went for these to give me setup options. Useful when I have no idea how this will work!

Rear end parts. 3x25mm step shaft, M3 grub screw to hold the shaft in place, uprights (with some place holder old bearings in) and TA01 hubs.

Trial fit of the driveshaft. 42mm was a good guess. I have a stray 39mm shaft from that TA01 I had and its definitely too short. Based on what I can glean from touring car kit that would mean you need the 44mm swing shaft if you want to run universals.

All installed with the ball screws for the camber link set to give the longest arm for hopefully most rear grip. I ran into the camber arm catching another part limiting droop issue as I did on the front. This is on the inner end so I could potentially solve by moving to the outer position or adding a spacer. The turnbuckles are 20mm m chassis from 3 racing from the spares box. I still had to cut 5mm off the rod ends to get it short enough.

For the shock I drained the oil and dry fitted. With the short eyelet (87mm length) its still too long. I popped the 3mm spacer inside and tried again but it was still a bit long. I went to the large 7mm spacer and it definitely all fits together but I am a little concerned there is not enough droop and too much up travel. Again, need to wait for wheels. Click on the image for video

This went together MUCH more simply than the front. No modifications to parts, just appropriate spacers here and there. Going to need another set of 3mm ID spacers though. Using loads and got the whole other side of the car to do yet.

Next will be tearing down the gearbox and rebuilding the ball diff. Never managed to get a ball diff reliably working before, but want to give this a go seeing as I have it.

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Last one for today. I decided to fit the rest of the suspension and put it on some buggy wheels to see what things looked like. Glad it did!

I was concerned about the lack of droop at the front for ground clearance, and it shows that you really shouldn't eyeball camber! I put it on the wheels and the reason the front c hubs were hitting the arms was because it had about 10 deg negative camber! I also ran into the problem of the amount of travel popping the ball ends off so I needed to find a way of turning the inner ball horizontal so it could rotate more.

I opened out the turnbuckles to get the wheels about vertical and ran out of thread! I switched them to the 3x32 turnbuckles from the TT02B set I have and they worked perfectly. Once the wheels were vertical the droop was much more because the c hubs weren't at such an angle so weren't fouling the arms. There was so much droop the shocks wouldn't reach! I switched the eyelets to the long rear eyelets which are 1mm longer and added a nut to space them. They are now 73mm long.

I found a couple of random looking holes on the shock towers so I threaded some ball screws into them and they seemed to work

They upper arms are about parallel with the lower arms.

Here is how it looks

At the rear it all looked pretty good. There is more ground clearance at the rear than the front but with no motor and electronics installed I will leave it for now.

Here is how it looks under load

This is about it for a while. The TRF201 steering parts I need are on special order from Tony but will be a few weeks. I should get my rally wheels soon and I need to sort the diff too.

Having been out in the snow again and spotted a kid driving his rc truck around I have got thinking about running this waterproofed. Brushed motor, waterproof ESC and servo, balloon over the Rx. Any suggestions most welcome!

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@Juls1 Possibly. I did look at that combination as I have some spare 50601 front piston shafts. However the longest they will build is 81mm. This is set on the middle arm hole too so I can move it out one more to lower ride height and reduce travel a little. As I say, it's all parked until there is a motor and some proper weight on that end of the car. It's possible the springs are too preloaded as they are compressed slightly by the shorter build of the shock. Annoyingly because the rear CVA are 11mm bore not 10mm the front TRF201 spare springs I have don't fit. If needs be I can get the Traxxas spring collar and use the Core RC progressive big bore springs as there are shorter and available in lots of sizes, the clear the shock body and use the regular size spring plactform at the bottom. I have a set on my Grasshopper 2 Ultra G.

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The﻿ car currently has the standard TRF201 anti squat geometry built in at about 2 deg I think. I can shim it out but why would﻿ I want to? Interested to know your thoughts here. ﻿﻿﻿

I didn't mean anti-squat angle of rear arms, but angle of swing shafts. From your pictures, it seems that they are angled forward, which adds to anti-squat effect. I noticed this effect when i tried to "cheat", using DF03RA rear arms to shorten wheelbase. Car acted really weird with so much anti-squat.

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I didn't mean anti-squat angle of rear arms, but angle of swing shafts. From your pictures, it seems that they are angled forward, which adds to anti-squat effect. I noticed this effect when i tried to "cheat", using DF03RA rear arms to shorten wheelbase. Car acted really weird with so much anti-squat.

Interesting point. I didn't know that. The arms are in their rearmost position so there is no way to improve that as the 3 deg of toe in that sweeps them forward is both useful for a rear drive and built into the chassis.

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A little more today. Some steering parts have come up which has moved the front end along a bit.

Base plate and 630 bearings installed

L parts with 730 bearings installed.

Fairly short distance to the steering arms. At least to me being used to buggies

Ball to all distance is roughly 40mm

The steering arms are a lot lower than the rack so a fair amount of spacing will be needed to prevent bump steer

But of trial and error, but got there. M3 x 16 screws in the steering arms with a 3mm cva shock spacer then a ball nut. 3 x 23mm turnbuckles from the TT02B set. Had to cut the ball joints down by around 5mm each to be able to make them short enough. Turned out to be more like 43mm centres once everything was squared up.

Bump steer appears minimal and there definitely seems to be some ackerman effect too. Fingers crossed